In general, a battery module includes a plurality of cells connected in series and/or in parallel. The battery module is typically produced in a shape shown in FIG. 1. FIG. 1 illustrates a battery module including a cell assembly 10 including a plurality of cells arranged in a direction, and a case 20 having end plates 21 capable of surrounding the cell assembly 10.
However, when the battery module is swollen due to cell overcharge or the like, the cell assembly 10 is deformed and, at the same time, the end plates 21 at two sides thereof bulge and expand outwards as illustrated in FIG. 2.
Although an inner margin of the battery module may be previously ensured in consideration of the expansion problem, the margin causes an increase in module size and thus may not serve as a proper solution.
Alternatively, a technology of suppressing expansion of a battery module by providing rigid end plates at two sides of a cell assembly is commonly used. However, when expansion of the battery module is forcibly suppressed, cell lifetime (e.g., the state of health (SOH)) may be reduced. That is, expansion should be allowed by a certain degree and lateral maximum displacement due to the expansion should be limited.
As a technology related to swelling of a battery module, Japanese Patent Publication No. 2005-108693 discloses a battery pack capable of preventing changes in the location of the center of laminated cells and the location of electrode terminals by absorbing of a thickness variation of the laminated cells based on elastic transformation of an elastic part when the thickness variation occurs due to a variation in the internal pressure of the laminated cells.
Korean Patent Publication No. 2007-0025734 discloses a secondary battery module capable of preventing bending deformation due to volume expansion of unit batteries, by providing bent parts on end plates of the secondary battery module.
In spite of the disclosure of the above technologies, a technical means capable of allowing a certain degree of expansion of end plates due to swelling and of controlling lateral displacement of the end plates due to the expansion to an appropriate level has not been disclosed and thus a solution thereto is required.